1. Field of the Invention
The present invention relates to an ink jet recording apparatus having a head recovery means and a recovery method thereof.
2. Related Background Art
Among recording systems for printers and the like, the ink jet recording system which performs recording on a recording medium by allowing ink to discharge from a discharge port (nozzle) has been widely adopted in recent years since it is a low-noise non-impact recording system which allows for a high-density and high-speed recording operation.
The ordinary ink jet recording apparatuses comprise driving means for driving a carrier which mounts a recording head (recording means), conveying means for conveying a recording paper, control means for controlling these means and the like. There are also available recording apparatuses such as those which apply pressure on the ink by using an electromechanical converter such as piezoelectric element, or those which irradiate electromagnetic wave such as a laser on the ink to heat the ink and, by this heating, allow the ink to bubble, or to allow the ink liquid to generate heat by the electromechanical converter having a heating resistance element and to bubble the ink liquid to generate energy for discharging ink from discharge ports of the recording head. Among them, the ink jet recording apparatuses of a system for discharging ink droplet by utilizing thermal energy can make a recording of high resolution since discharge ports can be arranged in high density. In particular, the recording head which uses an electromechanical converter element as an energy generating element can be easily made compact and, by applying the IC technology and the micro processing technique which have remarkably advanced in technology and reliability in the recent semiconductor manufacturing field, high density mounting by taking a full advantage of its merit can be made easy and the manufacturing cost thereof can be also reduced.
Such an ink jet recording apparatus is provided with a head recovery means for preventing a printing failure due to clogging in the discharge port. One of this head recovery means is such that, by covering a head with a cap, the ink is sucked from the discharge port by a suction pump through the cap so that high viscosity ink and minute contaminants in the inside of the recording head and ink supply flow path as well as bubbles in the ink are sucked from the top of the discharge port. The other one is such that the head surface is wiped by a flexible wiper blade so that fine contaminants and residual ink are removed and the head surface is put into a clean state. Another one is such that the recording head discharges a small amount of ink immediately before performing recording so as to maintain a steady discharge.
In the ink jet recording apparatus for printing while allowing these recording heads mounted on a carrier to reciprocate, a large capacity ink tank is required to reduce exchange frequency of the ink tank. In a simple constitution of mounting the recording head and the ink tank integrally on the carrier, since inertia of the ink tank mounted on the carrier increases, there has been known a method, wherein the ink tank is separated from moving parts such as the carrier and is fixedly arranged and a tube and the like is connected to the recording head on the carrier so as to supply the ink.
In such an ink jet recording apparatus, in order that the ink does not drop from the recording head at other than print driving, a minute negative pressure to an atmospheric pressure is always applied so that the ink discharge for printing and useless ink dropping prevention become compatible. However, when influenced by reciprocating movement of the carrier at the print driving in this state, the ink inside a connection tube flows to push out the ink inside the recording head, or the ink is sucked inside the connection tube, thereby causing fluctuation in the discharge amount, printing irregularity and non-discharge.
As a countermeasure, there has been known a technology in which an air bank is provided in the vicinity of the recording head between the tube and the recording head and an air buffer container is installed, which buffers pressure fluctuation due to the ink flow inside the tube and stabilizes the discharge by utilizing elasticity of the air. This air buffer container takes the upper part as the air bank and the lower part as an ink bank and has a function also of separating the air from the ink inside the tube where the air is mixed and sending the ink only to the recording head. However, this air buffer container is required to secure a necessary liquid surface height of the ink bank in order that the air does not approach the inside of the recording head from the air bank due to vibration of the liquid surface of the ink bank by the reciprocating movement of the carrier.
Also, in the other system, which conveys a recording medium and prints without scanning the carrier, there is available a method in which the air buffer container similar to the above described is installed for the purpose of separating the air mixed inside the ink. In this case also, it is necessary to secure the necessary liquid surface height of the ink bank inside the air buffer container.
The liquid surface height of the ink banks of these air buffer containers has a tendency to gradually fall by permeable approach of the air from the tube wall surface and bubble removal of ink dissolved gas and it is, therefore, necessary to continuously maintain the necessary liquid surface height. For example, regarding a maintaining method of the necessary liquid surface of the ink bank of the air buffer container in the ink jet recording apparatus which supplies the ink from one piece of the tube, there is a method in which a switching means is provided in the ink supply path and the ink supply path is closed so that the ink and the air inside the recording head are sucked by using the cap of the above described head recovery means and the suction pump and, after that, the ink supply path is opened and the ink is filled, thereby controlling the amount of reduced pressure inside the air buffer container so as to restore the necessary liquid surface.
The color ink jet recording apparatuses of recent years have become capable of full-color recording by using multi-color ink and discharging the ink from the discharge port corresponding to each color. Such color ink jet recording apparatuses reduce the distance among each discharge port as much as possible and perform suction recovery of a plurality of colors by the same cap for the purpose of miniaturization of the apparatus, improvement of impact accuracy of the ink on the recording paper and reduction of recording time by reduction of moving distance of the carrier.
When the cap is removed from the recording head after the discharge ports of a plurality of colors are sucked and recovered by the same cap, the ink which was mixed inside the cap adheres on the surfaces of the discharge ports of the recording head and flows inside the recording head from the discharge ports by minute negative pressure due to the above described ink dropping prevention and causes color mixing so that recording quality is remarkably deteriorated.
In order to solve such a trouble, it is necessary to prevent the ink from depositing on the discharge port surface of the recording head. Hence, for example, as disclosed in Japanese Patent Application Laid-Open No. 60-151059, there is adapted a method in which the cap and an air intake valve are connected to the tube and, by opening this air intake valve, the inside of the cap is communicated with the air to suck the ink remaining inside the cap and, after that, the cap is separated. However, when the air intake valve is opened, the inside of the cap is put into atmospheric pressure, which generates differential pressure with the inside of the recording head and, furthermore, when the amount of ink inside the cap is large, there is a fear that the surface of the ink rises due to the flow of the air from the air intake valve and the ink adheres on the surface of the discharge port and generates color mixture.
Also, as disclosed in Japanese Patent Application Laid-Open No. 6-126947, there is adopted a method in which a gap is made by shifting the cap, and an empty suction is performed and, after that, the position of the cap is changed and, with the surface of the discharge port of the recording head put in a completely leaked state, the empty suction is further performed. According to these methods, a rise of the ink surface due to flow of the air is not generated, but the empty suction is required twice and, during that time, there is a fear of generating flow of the ink inside the recording head and mixing of color.
Particularly, as described above, in the case where the liquid surface restoring operation inside the air buffer container is performed and the ink suction is performed by the same cap, when there is an irregularity in the ink amount inside the air buffer container of each color, an irregularity of the negative pressure inside the recording head is generated, and there has been a fear of the ink mixed inside the cap flowing backward from the discharge port and flowing inside the recording head.
One of the objects of the present invention is to provide an ink jet recording apparatus and its recovery method, for which there is no fear of depositing the ink on the discharge port surface from inside a cap without making the constitution and the process complicated.
Another object of the present invention is to provide the ink jet recording apparatus which discharges the ink from the discharge port provided in the discharge port surface of recording means having the cap closely contacted the discharge port surface to cover the discharge port, suction means for performing suction from the discharge port through the cap closely contacted the discharge port surface, gap forming means for partially generating a gap between the cap and the discharge port surface, and a communication valve which allows the inside of the cap to communicate with the atmosphere.
According to this constitution, flowing backward of the ink inside the cap to the inside of the discharge port and closely contacting the discharge port again of the ink sucked and mixed inside the cap can be prevented and reduced. Furthermore, even when the ink adheres on the discharge port surface, the ink can be sucked and removed and it is, therefore, possible to prevent the mixture of the ink inside the discharge port and maintain the recording quality of high quality.
It is preferable that supply path switching means for switching the supply path for supplying the ink to recording means is further provided.
Space forming means may contain angle correction means for correcting the angle of the cap and separating means for acting on the angle correction means to separate one end side of the cap from the discharge port surface. This constitution uses the angle correction means of the cap conventionally provided to allow the cap to adhere on the discharge port surface and it is, therefore, not necessary to provide a special mechanism as the gap forming means.
Recording means has a plurality of discharge port columns provided generally in parallel and discharges the ink of different color for each discharge port column, and the cap may collectively cover a plurality of discharge port columns in common.
A communication portion with the suction means of the cap is provided at the one end portion side in relation to the longitudinal direction of the discharge port columns, and it is preferable that the communication portion with the communication valve of the cap and the gap formed by the gap forming means are provided at the other end portion side in relation to the longitudinal direction of the discharge port columns. According to this constitution, the ink suction and the ink flow inside the cap due to flow-in of the atmosphere are generated in the longitudinal direction of the discharge port and it is, therefore, possible to prevent the ink from flowing into the direction to cross over each discharge port of the ink and mixing.
Still another object of the present invention is to provide the recovery method of the ink jet recording apparatus which discharges the ink from the discharge port provided on the discharge port surface of the recording means having a suction step of sucking the ink from the discharge port by the suction means in a state of the cap closely contacting the discharge port surface, a first exhaustion step of creating a gap between the cap and the discharge port surface and exhausting the ink inside the cap by the suction means and a second exhaustion step of putting the communication valve for communicating the inside of the cap with the atmosphere in a communication state, closely contacting the cap to the discharge port surface and exhausting the ink inside the cap by the suction means.
According to this constitution, flowing backward of the ink inside the cap to the inside of the discharge port and closely contacting the discharge port again of the ink sucked and mixed inside the cap can be prevented and reduced. Furthermore, even when the ink adheres on the discharge port surface, the ink can be sucked and removed and it is, therefore, possible to prevent the mixture of the ink inside the discharge port and maintain the recording quality of high quality.
It is preferable that the suction step has the suction means to perform the suction when the supply switching means, in which the cap adheres on the discharge port surface and switches the supply path of the ink to the recording means, is in a closed state and, after that, has the supply path switching means to be put in an open state.
It is preferable that the suction ability of the suction means is decreased substantially at the same time when the supply path switching means is put in an open state. According to this constitution, the negative pressure inside the cap is always maintained larger than the negative pressure inside the recording means so as to prevent the ink from flowing backward to the inside of the discharge port and, at the same time, the suction ability is decreased so as to reduce the differential pressure between the inside of the recording head and the atmosphere and it is, therefore, possible to prevent breakdown of meniscus of the discharge port, backward flow of the ink and mixture of the ink when the gap is created between the cap and the discharge port surface.
In the first exhaustion step, it is preferable that the suction ability of the suction means is increased substantially at the same time when the gap forming means forms a gap between the cap and the discharge port surface. According to this constitution, the suction time can be shorten and extra ink deposited on the discharge port surface can be quickly sucked and it is, therefore, possible to prevent mixture of the ink to the inside of the discharge port.
According to the present invention, flowing backward of the ink inside the cap to the inside of the discharge port and closely contacting the discharge port surface again of the ink sucked and mixed inside the cap can be prevented and reduced. Furthermore, even when the ink adheres on the discharge port surface, the ink can be sucked and removed and it is, therefore, possible to prevent mixture of the ink inside the discharge port and maintain the recording quality of high quality.
When the gap forming means contains the angle correction means for correcting the angel of the cap and the separating means for acting on the angle correction means to separate one end side of the cap from the discharge port surface, the angle correction means of the cap conventionally provided to allow the cap adhere on the discharge port surface is used and it is, therefore, not necessary to provide a special mechanism as the gap forming means and its constitution becomes simple.
When the communication portion with the suction means of the cap is provided at the one end portion side in relation to the longitudinal direction of the discharge port columns and the communication portion with the communication valve of the cap and the gap formed by the gap forming means are provided at the other end portion side in relation to the longitudinal direction of the discharge port columns, the flow inside the cap due to suction of the ink and flow-in of the atmosphere is generated in the longitudinal direction of the discharge port and it is, therefore, possible to prevent the ink from flowing in the direction to cross over each discharge port and mixing.
When the suction ability of the suction means is decreased substantially at the same time when the supply path switching means is put in an open state, the negative pressure inside the cap is always maintained larger than the negative pressure inside the recording means so as to prevent the ink from flowing backward to the inside of the discharge port and, at the same time, the suction ability is decreased so as to reduce the differential pressure between the inside of the recording head and the atmosphere and it is, therefore, possible to prevent breakdown of meniscus of the discharge port, backward flow of the ink and mixture of the ink when a gap is created between the cap and the discharge port surface.
In the first exhaustion step, when the suction ability of the suction means is increased substantially at the same time when the gap forming means forms a gap between the cap and the discharge port surface, the suction time can be shorten and, at the same time, extra ink deposited on the discharge port surface can be quickly sucked and it is, therefore, possible to prevent mixture of the ink to the inside of the discharge port.